It is known to provide insulation material as a sheet material i.e. in the form of a thin sheet which is then wrapped around an object to be insulated. It is also known that the sheet material comprises nanoparticle filler within a polymer matrix. For example, an electrical conductor may conventionally be insulated by wrapping around it an insulating tape comprising a nanoparticle filler within a matrix of polyesterimide (PEI), after which the tape is heated up in order to melt an adhesive applied on it and to thereby glue the tape on the conductor. This conventional insulation system is well resistant against partial discharge, this resistance being based on the nanoparticles' ability to prevent the charged particles from penetrating the insulating tape.
It is further known e.g. from EP0356929 to protect underlying parts of an insulation system against corona discharge by providing the insulation system with an electrically conducting top layer. The top layer may comprise a chromium oxide (Cr2O3) filler in a polymer matrix. The Cr2O3filler increases the electrical conductivity on the surface of the insulation system, and this appears to mitigate the concentrated effect of a corona discharge. It is believed that the conductivity causes the effect of the corona discharge to be dissipated over a larger surface, thus reducing the detrimental effect of the same.
While the two aforementioned insulation systems, the nano-filled tape and the Cr2O3-filled top layer, both provide a satisfactory resistance against partial discharge, there is a constant desire to further improve this resistance in order to prolong the lifetime of the insulation system.
While some insulation systems are available in the form of a sheet material, there are no sheet materials available for putting together an advanced insulation system. For example, the Cr2O3-filled top layers are applied on the conductor in a complicated process during which the conductor passes multiple times through a coating bath, subsequent wiping dies or felts, and a heating device for curing the coating. This conventional coating process can therefore be implemented solely by highly specialized companies with corresponding equipment.